1. Field of the Invention
The present invention illustrates a high voltage protection system, and more particularly, the high voltage protection system for adjusting duty cycle by using pulse width modulation signal.
2. Description of the Prior Art
With the advancement of techniques, various electric devices with high operational performance are widely adopted. Nowadays, most electric devices are required to perform high processing speed and low response time in conjunction with a high-level processor integrated to a micro volume circuit. Thus, the electric devices can be operated by users anytime and in anyplace. For example, the specification of iPhone 5s uses an A7-typed processor. The specification of iPhone 6 Plus uses an A8-typed processor. Another example is that the central processing unit (CPU) of the personal computer is upgraded from Intel® Core™ i5 to Intel® Core™ i7. Specifically, power consumption and heat generation of the electric device are increased since the clock frequency of the processor is increased. Thus, the performance of heat dissipation components such as heat dissipation fans, a water cooling system, thermally conductive adhesive, and a heat sink attracts more attention. Among these heat dissipation devices, a water cooling system has the best heat dissipation performance yet has a large circuit volume, high cost, and high noise. Thermally conductive adhesives and heat sinks have smaller volume with inferior heat dissipation performance since they only use a medium for conducting heat. As a result, heat dissipation fans became the most popular devices for dissipating heat in general electric devices.
Generally, when the electric device is used, unstable voltage or an extremely high voltage pulse may be received by the electric device. For example, when the computer is used by a user, the voltage of the AC/DC source may be unstable because of lightning. When the notebook is used by a user, the voltage of the batteries may be unstable because the batteries are expired. When the electric device is activated by the user, a wrong voltage may be received since the user puts the plug in the wrong socket. Thus, two protection circuits are introduced in the conventional heat dissipation fan circuit in order to avoid the heat dissipation fan being damaged by the unexpected high voltage. The first protection circuit includes an over voltage protection circuit (OVPC). When the unexpected high voltage is received, the OVPC cuts the power of the fan circuit. Since operation of the fan circuit is paused due to the power cut, the fan circuit is protected. However, when operation of the fan circuit is paused, the fan circuit cannot perform heat dissipation. As a result, when the unexpected high voltage is received, the fan circuit with OVPC is paused, thereby leading to damage of device (i.e., CPU) which needs to dissipate heat since the function of heat dissipation is also paused. The second protection circuit includes a voltage regulator (VR). When the unexpected high voltage is received, the VR transfers the high voltage to a regular voltage for protecting the fan circuit. However, when the fan circuit is operated under large current, the power tolerance of VR has to be increased, thereby leading to a large circuit size of VR.